In the past, flyweight centrifugal governors have been extensively used to control the speed of rotary, pneumatic, or pressure fluid driven high speed grinders and other tools. Typically, these flyweights have been revolved about a pivot point or displaced radially as the speed of the grinder increased by means of various linkage. The movement of the flyweights working against a spring as a speed reference force was converted into a movement of a valve means to modulate the supply of pressure fluid. Numerous ingenious devices have been developed to accomplish what appears to be this relatively simple task. However, unless the valve means itself was allowed to rotate, such centrifugal devices were subject to wear in use and over a period of time had a tendency to change the governor's ability to control speed. In many recent governors, the valving mechanism is allowed to rotate with the governor weights resulting in an improved mechanism. However, these devices are often cumbersome and have a valve member which may rub against a stationary part.
In addition, the above governing devices, because of the nature of their construction, are subject to seizing because of particles or moisture in the pressure fluid, mechanical linkage failure, or misalignment, any of which could result in dangerous overspeed of the grinding wheel.